Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by engines such as IC engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) system which includes a catalyst formulated to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3).
Generally, a reductant such as a diesel exhaust fluid (e.g., an aqueous urea solution) is inserted into the aftertreatment system as a source of ammonia. The reductant facilitates the decomposition of the constituents of the exhaust gas by the catalyst included in the SCR system. The delivery of the reductant into conduits of the aftertreatment system is generally assisted by the exhaust gas flow to achieve efficient mixing of the reductant with the exhaust gas and reduce reductant deposits.
One or more injectors which can be included in a reductant injection assembly are used to insert the reductant into the exhaust gas stream. Large engines produce significant amounts of exhaust gas, and thereby need large volumes of reductant to be inserted into the exhaust gas stream. This is generally achieved by using multiple injectors to insert multiple reductant streams at multiple points in the exhaust gas flow. However, exhaust gas assisted delivery of reductant, which is commonly used for reductant insertion and is optimized for insertion of reductant via single injector, does not transition similarly to multi point injection of the reductant.
Simply increasing the number of insertion points can lead to poor reductant spray characteristics, poor delivery and inefficient mixing of the reductant with exhaust gas flow, for example due to cross-flow at the insertion points, and unfavorable interactions of a first reductant spray at first insertion point with a second insertion spray at a second insertion point. This can lead to increased reductant deposits within the components of the aftertreatment system, thereby increasing backpressure. The increased backpressure and poor mixing can eventually lead to reduce NOx conversion efficiency, increased maintenance costs and ultimate failure of the aftertreatment system.